1. Field of the Invention
The present invention relates generally to the field of coal pulverizer mills and in particular to lubrication of internal bearings located in a gear box of a coal pulverizer mill, especially a B&W MPS-type mill.
2. Description of the Related Art
Coal pulverizer mills are used to grind coal for combustion in industrial power plants. B&W's MPS-type mills are one type of coal pulverizer which have been used for approximately the past thirty years. The B&W MPS mills use a rotating grinding mechanism to crush coal chunks into finer particles for combustion.
The coal grinding mechanism is driven by an electric motor through a gear reducer contained in a gear casing. The bearings inside the gear casing must be lubricated to prevent lock-ups and excessive wear on the bearing surfaces. Lubricating oil is used for this purpose. However, oil leaks at two bearing locations in the gear casing are a recurring problem with these gear casings.
As seen in FIG. 1, a bearing casing 10 has several bearing positions, two of which are known as bearing position four 30 and bearing position five 20. The oil leaks which occur in these types of bearing casings 10 occur at bearing positions four and five 30, 20. FIG. 2 shows a prior art gear casing configuration of the bearing positions 20, 30 from the side and helps to explain how the oil leaks occur. Each bearing position 20, 30 has a bearing cartridge 28, 38 with an annular groove 26, 36 around its circumference. Oil is supplied to each groove 26, 36 through oil tube 40 located between the bearing positions 20, 30. Oil moves from the grooves 26, 36 through an opening in the bearing cartridges 28, 38 into bearing top chambers 22, 32 of each bearing position 20, 30, respectively. To prevent oil from leaking out the top of the gear casing 10, an O-ring 24, 34 is provided around the top of each bearing cartridge 28, 38 above the annular grooves. Unfortunately, over time these O-rings 24, 34 harden and lose their seal between the gear casing 10 and bearing cartridges 28, 38.
Conventionally, this oil leak problem has been solved by stopping oil flow to annular grooves 26, 36, redirecting the oil flow from a manifold 200 (not shown in FIG. 2) through a pair of external hoses, connected to covers 21, 31 and into bearing top chambers 22, 32. Several parts are required to effect this alteration to the oil flow path. This solution is not entirely satisfactory since external hoses present in an industrial setting, such as a power plant, are subject to being cut, corroded, crimped or otherwise damaged. Further, due to the complexity of the alteration of the oil flow path involved, it is not uncommon for the alteration to be made incorrectly, which can lead to continued oil leaks and failure of the bearings.